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#!/usr/bin/env python
"""Amend systemd-repart definiton files.
In order to avoid Import-From-Derivation (IFD) when building images with
systemd-repart, the definition files created by Nix need to be amended with the
store paths from the closure.
This is achieved by adding CopyFiles= instructions to the definition files.
The arbitrary files configured via `contents` are also added to the definition
files using the same mechanism.
"""
import json
import sys
import shutil
from pathlib import Path
def add_contents_to_definition(
definition: Path, contents: dict[str, dict[str, str]] | None
) -> None:
"""Add CopyFiles= instructions to a definition for all files in contents."""
if not contents:
return
copy_files_lines: list[str] = []
for target, options in contents.items():
source = options["source"]
copy_files_lines.append(f"CopyFiles={source}:{target}\n")
with open(definition, "a") as f:
f.writelines(copy_files_lines)
def add_closure_to_definition(
definition: Path, closure: Path | None, strip_nix_store_prefix: bool | None
) -> None:
"""Add CopyFiles= instructions to a definition for all paths in the closure.
If strip_nix_store_prefix is True, `/nix/store` is stripped from the target path.
"""
if not closure:
return
copy_files_lines: list[str] = []
with open(closure, "r") as f:
for line in f:
if not isinstance(line, str):
continue
source = Path(line.strip())
target = str(source.relative_to("/nix/store/"))
target = f":/{target}" if strip_nix_store_prefix else ""
copy_files_lines.append(f"CopyFiles={source}{target}\n")
with open(definition, "a") as f:
f.writelines(copy_files_lines)
def main() -> None:
"""Amend the provided repart definitions by adding CopyFiles= instructions.
For each file specified in the `contents` field of a partition in the
partiton config file, a `CopyFiles=` instruction is added to the
corresponding definition file.
The same is done for every store path of the `closure` field.
Print the path to a directory that contains the amended repart
definitions to stdout.
"""
partition_config_file = sys.argv[1]
if not partition_config_file:
print("No partition config file was supplied.")
sys.exit(1)
repart_definitions = sys.argv[2]
if not repart_definitions:
print("No repart definitions were supplied.")
sys.exit(1)
with open(partition_config_file, "rb") as f:
partition_config = json.load(f)
if not partition_config:
print("Partition config is empty.")
sys.exit(1)
target_dir = Path("amended-repart.d")
target_dir.mkdir()
shutil.copytree(repart_definitions, target_dir, dirs_exist_ok=True)
for name, config in partition_config.items():
definition = target_dir.joinpath(f"{name}.conf")
definition.chmod(0o644)
contents = config.get("contents")
add_contents_to_definition(definition, contents)
closure = config.get("closure")
strip_nix_store_prefix = config.get("stripNixStorePrefix")
add_closure_to_definition(definition, closure, strip_nix_store_prefix)
print(target_dir.absolute())
if __name__ == "__main__":
main()
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